Polycarbonate is widely used owing to its excellent mechanical characteristics such as impact resistance as well as high heat-resistance, transparency, etc. Aromatic polycarbonate has recently been used for recording materials such as optical disks and the demand has been increasing sharply.
Known methods for the production of such polycarbonate include the direct reaction of an aromatic diol such as bisphenol A with phosgene (the interfacial polymerization method) and the transesterification reaction of an aromatic diol with a diaryl carbonate such as diphenyl carbonate (the melt method).
Regarding polycarbonate produced by the above methods, U.S. Pat. No. 5,521,275 discloses a process for converting the molecular weight of an aromatic polycarbonate in the presence of a catalyst using an extruder with a polymer seal section and a venting section under a reduced pressure, and European Patent No. 0,595,608 discloses a process for reacting several kinds of diaryl carbonates in the conversion of the molecular weight. However, the processes disclosed in these patent specifications cannot significantly increase the molecular weight of polycarbonate.